Inhibitor



' Where the metal is not covered by scale.

' inhibitors for these purposes.

Patented Oct. 15, 1940 UNITED STATES PATENT OFFICE W. Cupt, Jr., Enid, Okla., assgnors to General Chemical Company, New York, N. Y.,` a corporation of New York Application February 21, 1940, seria1No.'32o,o35

14 Claims.

This invention relates to corrosion inhibitors, to inhibited acid compositions, to methods for pickling metals for the'removal of oxides or'mill scale, and to pickling baths. The invention is more particularly directed to inhibitors, inhibited acid solutions and pickling baths comprising or containing sulfur bearing oils soluble in Water and in dilute inorganic acid solutions and derived from sludges formed in oil refining processes in which sulfuric acid is employed. The invention is also especially directed to metal pickling processes carried out with utilization of such soluble sulfur bearing oils as corrosion inhibitors.

Pickling solutions for removing oxides or mill scale from the surface of metals ordinarily consist largely of a dilute solution of an inorganic acid such as sulfuric acid. The acid, although it dissolves the oxides and scale, also attacks the metal to some extent so that acid is consumed, and a certain amount of metal is lost. It also appears that hydrogen liberated by the action of the acid on the metal has a serious embrittling effect upon the metal being treated. Inhibitors are also used to prevent pitting and corrosion In.. hibitors are commonly employed in such solutions to decrease acid activity with respect to the metal without greatly affecting the solvent action of the solution with respect to oxides.

The principal objects of the invention are directed to provision of improvements in inhibited acid compositions, methods for pickling metals, pickling baths, and to provision of markedly effective water soluble sulfur bearing oil corrosion It is a further aim of the invention to provide water soluble sulfur bearing corrosion inhibitor oils having a relatively high sulfur content substantially all of which is in strong chemical combination, and which oils are stable and do not become turbid or deposit sulfur on standing.

In oil refining pocesses, involving sulfuric acid treatment of petroleum distillate oils obtained from sulfur containing crudes, large quantities of sludges are produced. Ondissociation by heating, these sludges form gas mixtures containing water vapor and condensable hydrocarbon vapors, and gases such as sulfur dioxide, carbon dioxide, nitrogen and uncondensable hydrocarbons. On cooling such gas mixtures, for example to about normal temperature, there are obtained crude sulfur oil condensates herein referred to as initial sulfur oils. which are sulfur bearing oils containing sulfur constituents of variable types and quantities depending largely upon the nature of the sludge material. These sulfur constituents and other ingredients are so complex that accurate analysis by known methods has not been possible. The crude sulfur oils are insoluble in water and in dilute acid solutions. Further, in instances such oils are objectionabiy odorous.

Sulfur oils of this type are of such nature that a substantial portion of certain water insoluble sulfur constituents contained in or derived from crude or initial oils may be converted-for example by subjecting such constituents to the action of oxidizing agents-to Water soluble substantially odorless form. In accordance with the present invention, we have found that sulfur bearing oils containing certain water soluble sulfur constituents and resulting from such oxidation treatment, possess properties rendering these oils especially suited for inhibiting the corrosive action of acids on metals.

A further appreciation of the objects and advantages of the invention may be had from a consideration of the following description of the water soluble oils constituting the improved corrosion inhibitors, of inhibited acid compositions and pickling baths containing the improved inhibitors, of pickling methods involving use of the improved sulfur bearing oil inhibitors, and of methods for making the improved inhibitors. The accompanying drawing illustrates diagram- .matically apparatus by which the improved water soluble sulfur bearing oil inhibitors may be made.

Referring to the drawing, I indicates the combustion chamber of a furnace adapted to burn any suitable fuel. In chamber I0 is a kiln II, for example a xed shell provided with suitable mechanism to facilitate discharge of coke. A rotary retort may be employed if desired. Preferably, an externally heated kiln adapted to substantially exclude admission of air is used. One end of kiln II communicates with a gas outlet I3, and the opposite end projects into a header Il into which solid residue of the sludge is continuously discharged. Header I4 empties into air-lock I 5 through which coke may be discharged without admitting air to the kiln. Siudges are run into the kiln from tank I1 through pipe I8. Outlet I3 is connected to condenser 20 the condensate of which drains into a separating tank 2l through pipe 22. Gases uncondensed in cooler 20, containing principally sulfur dioxide, are discharged through gas line 23. Separator 2l may be large enough to permit continuous gravity separation of water and oil contained in the condenser condensate. Sulfur bearing hydrocarbon oils are withdrawn through pipe 25 discharging into collecting tank 26.

Still 30 may be externally heated by hot combustion gases generated in brickwork setting 3|. Crude condensate from tank 26 is run into the still through pipe 38, controlled by valve 39. Vapors generated in the still flow through line 4| to a condenser 43, the condensate of which drains through pipes 45 or 46 into receivers. 50 or 5|.

In producing the improved water soluble sulfur bearing oil inhibitors, acid sludges which may be used to advantage are those resulting from sulfuric acid treatment of distillate oils obtained from petroleum crudes containing sulfur. Sludges employed are preferably those formed by sulfuric acid treatment of light hydrocarbon oil distillates such as gasoline and kerosene, containing not less than about 0.15% sulfur, al-

y though distillates containing less sulfur may be utilized if desired. Examples of distillate oils from which sludges are produced of a suitable character are straight-run gasoline distillates containing about 0.15% sulfur or more, and cracked distillate averaging 0.25 to 0.30% sulfur or more.

Sludge material, which may have for example a titratable acidity of 40% to 60% expressed as HzSOi, is continuously fed into kiln Il. Burners in furnace I0 are adjusted to maintain within the kiln temperatures desirably not in excess oi about 750 F., as above this temperature the sulfur oils constituting basis of the improved inhibitors tend to be decomposed. The preferred temperatures are about 250 F. at the sludge inlet end, and about 500 F. to 600 F. at the coke outlet end of the kiln. The sludge is relatively gradually heated through the preferred temperature range, and free and/or combined sulfuric acid of .the sludge is reduced to sulfur dioxide by the hydrogen of the hydrocarbons and/or by the carbonaceous matter contained in the sludge. The sludge is thus dissociated with production of water vapor, and hydrocarbon vapors and sulfur compounds are formed. Residual coke is continuously discharged from the kiln through air-lock I5. The major part of the sulfur oils appears to have been evolved by the time the sludge has reached a temperature of S50-400 F.

The gas resul-ting from sludge dissociation contains principally water vapor and sulfur dioxide, substantial amounts of condensable hydrocarbons and sulfur compounds, and smaller quantities of uncondensable hydrocarbons and gases such as carbon dioxide, carbon monoxide, and nitrogen. Sludges of the kinds mentioned produce from say 5 to 15% condensable oils based on the weight of the original sludge. Preferably, sludge dissociation is effected in the kiln substantially in the absence of oxygen and in the absence of other extraneous gases, since the volume of gas formed is lessened and sulfur oil loss by volatilization is decreased. Hot gaseous and vaporous products of sludge dissociation pass into condenser 20 in which the gases are cooled to substantially room temperature. Cooling may be accomplished by circulating any suitable cooling liquid or gas through the condenser in indirect heat exchange relation with the retort gas mixture. On cooling, substantially all of the water vapor and the major portion of the condensable hydrocarbon vapors and sulfur compounds are condensed. condensate, containing varying proportions of Water, liquid hydrocarbons and sulfur compounds,

is drained into separator 2|. In the latter. the oils rise to the top of the liquid mass in the tank, and may be intermittently or continuously withdrawn through pipe 25 into tank 26 for collecting raw condensate or initial sulfur oil. Water settling to the bottom of the separator 2| is discharged through pipe 21.

Oil in tank 26 is a sulfur bearing oil containing generally from about 2 to sometimes upward of 25% sulfur, in strong chemical combination. Sulfur content may vary considerably in accordance with characteristics of the petroleum crudes and of the acid sludges produced on treatment of the hydrocarbon oil distillates with sulfuric acid. For example, a sludge formed by sul furic acid treatment of a straight-run gasoline yielded an oil condensate of 12% by weight oi the sludge, the condensate analyzing 14.8% sulfur. A cracked distillate sludge yielded 10% by weight of oil condensate having a sulfur content of 7.5%. In another instance, a cracked distillate averaging about .25 to .30% sulfur produced on treatment with sulfuric acid a sludge which, on treatment in accordance with the present method, yielded 10.8% by Weight of oil condensate analyzing 20.8% sulfur. While the surfur content of the initial sulfur oils may vary widely as indicated, experience shows these oils average about 20% sulfur by weight.

Initial sulfur oils thus obtained, while readily soluble in strong sulfuric acid, are relatively water insoluble. These oils are of such nature that a substantial portion of certain water insoluble sulfur constituents contained in or derived from an initial high sulfur oil of the type described may be converted, by the action of an oxidizing agent, to water soluble, practically odorless sulfur oils which may be recovered readily from the oxidation reaction mass. We have found these water soluble sulfur oils possess properties making such oils especially suited for inhibiting the corrosive action of acids on metals.

The hereafter detailed oxidation treatment of initial water insoluble sulfur oil to produce water soluble oil may be applied if desired directly to an initial sulfur oil as recovered in tank 26. Such oil contains appreciable quantities of foreign matter, such as coke-dust and tars, which under most circumstances preferably should be removed. Separation of foreign matter from initial oil may be effected by distillation producing a tarry still residue and a distillate sulfur oil. The oxidation treatment may be applied to the sulfur bearing oil of tank 26 after removal of the foreign matter.

fractions, e. g., a light or a heavy fraction, are

However. since different boiling range suited for different types of inhibitors, according to the more satisfactory procedure for making the inhibitor oils of the invention, it is preferred to (l) remove foreign matter from the initial sulfur oil of tank 26 by distillation; (2) simultaneously fractionate the initial oil during distillation to recover preferably a light fraction and a heavy fraction; (3) then subject such fractions to oxidation treatment.

To remove foreign matter from raw condensate of tank 26 and to split the condensate into two or more fractions, oils from tank 26 are run into still 3|] through line 38. It is preferred to fractionate to obtain a relatively light fraction containing oils distilling over at temperatures up to about 340 F., and a heavier fraction including oils boiling above 340 F. and preferably not above about 475 F. However. in some instances, the light fraction may contain oils boiling up to about 350 case of one initial sulfur oil, having a sulfur con# F., and the heavy fraction may comprise oils boiling from about 340 F. to desirably not more than 650 F. The distillation operation may be carried out in any suitable still, preferably one provided with equipment for collecting separate fractions of distillate. Steam, vacuum or straight re distillation may be used. The inhibitor of the invention most adaptable for general use is one obtained from a hereafter noted high boiling fraction. With respect vto this fraction, best yields are obtained by straight nre distillation of the oil of tank 26. By this mode of distillation, yields of say Bti-% by weight (based on oil fed into the still) -of high boiling fraction are obtained. l H

Externally heated still 30 may be operated at one atmosphere pressure to produce a rst cut including all oils-distilling over at temperatures up to about 340 F. Vapors are liquefied in cooler 43, and condensate run into receiver :50. In the tent of about 20% by weight, this low boiling fraction constituted about 46% by weight of the initial sulfur oil fed into still 30. When removal of low boiling fraction is substantially complete, temperature is raised to distill over as a second cut oils having boiling points ranging from about 340 F. up to preferably about 475 F. Vapors formed are condensed and recovered in receiver 5i. In this example the high boiling fraction comprised about 39% by weight of the initial crude sulfur oil introduced into still 30. Approximately 13% by weight or the initial sulfur oil remained in still 30 as a coke or asphalt residue, and the balance was lost as uncondensable vapors and gases. The cuts obtained had the following properties:

Cut 2 S. G, at 60 F Percent sulfur by weight Color Pour freely Light amber. Below zero F.

22.5 Pale yellow. Below zero F.

The low boiling cut in receiver 5l! usually contains a slightly higher percentage of sulfur than the higher boiling fraction of receiver 5I. If desired, all of the vapors evolved in still 30 may be condensed and collected in a single receiver instead of in two receivers as 50 and 5I. In this situation, the condensate collected corresponds in a general way with the condensate collected in tank 26 except that foreign matter, such as cokedust and tars, has been removed. ALittle is known of the exact composition of thesoils.- Generally described they are water insoluble, transparent and light-bodied, viscosity being around 32 to 34 Saybolt at 100 F. Color ranges from faint yellow thru light red. Sulfur content may vary from about 2 to in some cases upwards of 25% by weight, All of the sulfur is in strong chemical combination. It appears substantial amounts of the contained sulfur is present as alkyl suldes and possibly some disulfldes, and other sulfur bearing compounds. Specific gravity is usually less than one. On chilling or long standing, the oils do not become turbid or deposit sulfur. Water insoluble oils preferably such as above noted are subjected to the action of an oxidation agent to form the water soluble inhibitors of the invention.

It is possible to eiect conversion, to water soluble form, of water insoluble sulfur constituents contained in or derived from initial sulfur oils by subjecting such constituents to the action of oxidizing agents such as: hexavalent chromium compounds such as alkali metal dichromates and chromates, and chromic acid; alkali metal permanganates; and nitric acid. The hexavalent ide precipitate which materially interferes with a subsequent separation of insoluble oil and an I aqueous liquid containing the Water soluble oil.

Following is a specific illustration of such an operation using sodium dichromate as the oxidizing agent.

Example 1 In lead-lined tank 53 a water insoluble sulfur oil treating solution is made up by adding (all parts by weight) 31.5 parts of Na2Cr2Om2H2O to 756 parts of water, and then introducing 50 parts of 66 B. H2SO4 (93.2% HzSOi). About 59 parts of a high fraction (S40-475 F.) from receiver 5l and having sulfur content by weight of 16.5% are run through pipe 54 into lead-lined oxidation tank 5B preferably equipped with a high-speed lead-covered stirrer and an associated stationary lead boot with bottom perforations, thus insuring violent agitation and minimizing tarry matter contamination of the agitator blades. After starting vigorous agitation, oxidizing solution is fed in from tank 53 over a period of about 3 hours. At the end of about 7 hours, agitation is stopped, i. e., after a test portion of the mass in the oxidation tank indicated that reduction of dichromate is complete. Temperature during reaction was about 91 F. On completion of oxidation, the mass. in tank 56 comprises principally unreacted upon and hence water insoluble sulfur oil, water soluble sulfur oil formed by the oxidizing agent treatment, water, sodium sulfate and chromium sulfate both in solution, and variable amounts of brown tarry material carried in suspension. In the present example solids amounted to about 3% by weight of the reaction mass. The mass from tank 56 is run through a sand lter 58 to remove tarry and other solids, and the iiltrate is collected in a lead-lined separator 60. In the latter, the liquor is settled to thereby form an upper layer of unreacted water insoluble sulfur oil and a lower aqueous oxidation reaction product layer comprising chieiiy water soluble high sulfur oil, Water, and sodium and chromium sulfates in solution. After thorough settling the supernatant unreacted water insoluble oil is decanted off and the lower aqueous liquor layer is transferred. to neutralizing tank 62.

To the aqueous liquor in tank 62, dry soda ash is added with stirring in quantity to create slight alkalinity, e. g., pH of about 7.1. During neutralization the liquor is heated to about 170 F. to insure removal of CO2 and effect formation of a Cr(OH)a precipitate in readily lterable form. The neutralized oxidation solution is then pumped into a filter press 65 to remove chromium hydroxide from solution. The ltrate is charged into an evaporator 61, the filter cake washed with hot water and the washings combined with the filtrate. Alternatively, washings may be fed back into make-up tank 53 for use in a subsequent run. The iilter press mud, comprising principally chromium hydroxide. may be treated in any suitable way for recovery of chromium values.

Evaporator 61 is equipped with heating coils to which steam at approximate maximum of 250 F. is supplied. The aqueous mass is evaporated at atmospheric pressure preferably just to the point at which sodium sulfate tends to crystallize out. This procedure makes possible a relatively clean separation of oil and mother liquor and avoids formation of a mushy mass of crystals and adhering sulfur oil. During evaporation water is removed as steam. and water soluble sulfur oil collects at the surface, While the mother liquor consisting principally of a very nearly saturated solution of sodium sulfate containing possibly some sodium sulfate crystals and Cr(OH)a sinks to the bottom. From time to time water soluble sulfur oil product is decanted oi from the top of the mass in the evaporator and run through pipe 68 into a second separator 69. In the latter the oil is allowed to settle to drop out any small amounts of mother liquor and sodium sulfate which may crystallize. The final water soluble sulfur oil of the invention is drawn oil the top of separator 69 and fed into product tank 10. In some instances, during the evaporation operation a small amount of ilocculent Cr(OH)3 may separate out. Any of such precipitate carried out of the evaporator in the supernatant water soluble oil may be removed by means of a filter in line 68. Experience indicates, however, in the majority of cases such ltration is unnecessary. Evaporator mother liquor is run through wringer 15 to separate sodium sulfate crystals, and mother liquor from separator 69 and wringer 15, and wash water from wringer 15 are recycled through evaporator 61.

In the particular example, yield of water soluble sulfur oil was about 35% by weight based on the weight of the high. boiling fraction charged into oxidation tank 56. In other operations, using high boiling fractions, yields up to 65% have been obtained. Specific gravity of the product of the example under discussion was about 1.05, and the sulfur content by weight was 12%.

Low boiling fraction from received 50 may be subjected to oxidation treatment in a way similar to that described in Example 1. .In the case of low boiling fractions, yields of water soluble product are generally higher, amounting to as much as 75%. The oxidation treatments of the invention may also be applied to refined extracted water insoluble sulfur oils such as the products of Merriam and Cupit U. S. Patent 2,115,426 of April 26, 1938.

Example 2 Following is an illustration oi a method for making inhibitor oils of the inventionusing potassium permanganate as oxidizing agent. A treating solution is made up by thoroughly mixing (all parts by weight) about 43 parts of KMnO4 and 45 parts of 66 B. H2SO4 (93.2% H2SO4) with 1890 parts of water. The initial water insoluble sulfur oil used had a sulfur content of 22.5% by weight and was a condensate obtained by steam distilling a light hydrolyzed sulfur oil fraction (boiling below about S40-350 F.) made by the process disclosed in the Merriam and Cupit patent. While vigorously agitating, the oxidizing solution is added in small portions to about 23 parts of the water insoluble sulfur oil until the resulting mass becomes permanently pink in color. In this run. temperature was kept at about 45 F. by cooling. On completion of reaction, a

small amount of MnOa remaining in the mixture is dissolved by gassing with sufficient SO2 to produce a colorless solution. The mass is permitted to settle, and the aqueous oxidation solution (lower layer) containing water soluble inhibitor oil and unreacted water insoluble oil (upper layer) are separated by steam distilling oil the insoluble oil. 'I'he aqueous oxidation solution is evaporated and then treated with suicient ether to extract the water soluble oil from the aqueous residue. Ether is distilled out of the extract mass to recover the final inhibitor oil. In this instance. about 75% by weight of the sulfur oil treated was recovered as a water soluble sulfur inhibitor oil having a sulfur content of 17.5% by weight.

Example 3 About 50 parts (all parts by weight) of water insoluble sulfur oil similar to that used in Example 2 is treated at room temperature with 200 parts of 30% HNOs, the latter being added over a period of about 2 hours while vigorously agitating. The mass is settled and the aqueous oxidation solution (lower layer) containing water soluble product oil and unreacted water insoluble oil (upper layer) separated by decantation. The aqueous oxidation solution is neutralized with caustic soda, and then made slightly acid by addition of nitric acid. The resulting mass is treated with suicient ether to extract the water soluble oil from the aqueous residue. The ether extract is dried by use of anhydrous NazSO4, hydrated Nit-:S04 separated, and the ether distilled oi to recover ilnal inhibitor oil. In this run, about 22% by weight of the initial sulfur oil treated was recovered as water soluble sulfur oil having a. sulfur content by weight of 15.6%.

Compositions of the inhibitor oils made by the described procedures are complex and not definitely known. As far as we are aware, the inhibitor oils probably contain oxidation products such as sulfones in varying quantities depending upon the nature of the original sludge material and the particular mode of processing. Sulfur content ranges from about 11% to about 19% by weight. Speciilc gravity varies generally from one plus to about 1.07. The oils are practically odorless, and are soluble in water and dilute sulfuric, hydrochloric and nitric acids. The oils are transparent,

"and color ranges from pale yellow into light red.

Viscosity is low. of the order of 32 to 34 Saybolt at F. Chilling to zero (F.) does not affect stability or create turbidity. and sulfur does not settle out on long standing.

Reactions taking place during the water linsoluble sulfur oil treatment operations are complicated and are not understood. Belief is that some of the water insoluble sulfur constituents of the sulfur oils are oxidized to a Water soluble form. Our investigations show that temperatures at which the reaction is carried out, amounts of oxidizing agents used, and the acid concentration of the mass during the oxidation operation are features of importance. These factors in one way or another in some manner not understood affect yields of the desired final products. It is our belief excessive temperatures, or amounts oi oxidizing agents. or acid concentrations singly or in any combination cause what may be "over-oxidation" of some constituents of the oil being treated, bringing about increased formation of tarry-like solid material which apparently results in material decrease oi yield.

In all procedures for-making the inhibitor oils of the invention, temperature during treatment 75 operation should not exceed about 150 F. When using chromium compounds as oxidizing agents experience shows that most advantageous working temperatures are from about '70 to about 115 F. Generally, the higher the concentration of oxidizing agent and/or acid, the lower should be temperatures. When using oxidizing agents such as permanganates and. nitric acid, temperatures should be kept preferably at 'room temperature or less.

With regard to the amount of oxidizing agent used, in the case of chromium compounds and permanganates, oxidizing agent introduced should not exceed about 10% by weight of the reaction mass, e. g., the mass in an oxidation tank such as tank 56 of the drawing. When employing nitric acid, the HNOa concentration of reaction mass should not be greater than about 30% by weight. In one instance, where the HNO: concentration of the mass was about the reaction was vigorously exothermic and resulted in formation of much tarry material.

The presence of at least some sulfuric acid facilitates the oxidation reaction. Further, it is preferred to use sulfuric acid in amount at least suilcient to keep all chromium compound in solution, since in this way it is possible to secure best yields and most satisfactory overall operating conditions. 'Ihe same principles apply when using permanganates as the oxidizing agent; namely, desirably some sulfuric acid should be present in reaction mass and preferably enough to keep as much of the manganese as possible in solution. There may be instances, in the case of permanganates when, in spite of the presence of a theoretical sufficiency of sulfuric acid, some MnOz precipitate appears in the mass after oxidation is complete. In such instances, it is desirable to gas the mass with SO2 until all MnOz goes into solution. When using either chromium compounds or permanganates the sulfuric acid concentration of the reaction mass should not exceed about 15% by weight.

On account of the widely varying characteristics of the water insoluble sulfur oils which may be treated in accordance with the invention, it is not possible to state more fully than above as to the quantities of reagents to be employed in making the inhibitor oils of the invention. Having regard for the above discussed amounts of oxidizing agents and/or acids to be used, a few test runs on any particular Water insoluble sulfur oil will indicate to the operator the .most satisfactory quantities of' reagents for a given water in.- soluble sulfur oil.

Instead of decomposing the acid sludge by heating as described in connection with the drawing, the original acid sludge may be subjected to hydrolysis as by steaming with live steam, for say an hour, until separationof weak acid (sludge acid) and an upper acid tar layer takes place. The Weak acid may be drawn oi and the resulting acid tar or sludge material dissociated by heating as in a retort il. The oily distillate may be taken in two or more cuts if desired, although it is preferred to collect the oily distillate as in a tank 26. During steaming of the acid sludge a light-colored distillate may be recovered in a suitable condenser. This distillate and the condensate collected in tank 26 may beV separately treated as already described or may be hibiting properties. Since these oils are soluble in water and dilute acid solutions, their use as inhibitors in pickling baths and acid solutions, and in metal pickling processes afford the material advantage that they may be added in any desired way to the acid solutions to be inhibited.

The acid pickling baths with which the inhibitors of the invention are used may have acid concentrations of say 6 to 12%, such as are customarily employed in commercial pickling and cleaning operations. Sulfuric, hydrochloric, phosphoric, or hydrofluoric acids, or any other non-oxidizing acid, or acid sulfate baths may be used if desired. The amount of inhibitor oil added to the bath may be varied. As a rule only a small amount of oil is required. For example, the bath may contain from about l to about 20 pounds of the inhibitor per ton of 66 B. sulfuric acid. The pickling or cleaning operation may be carried out as in usual practice. The metal may be completely immersed in the acid or a solution of the pickling bath may be sprayed onto the surface of the metal and subsequently removed with a water spray. Concentration of the acid bath and temperature of the solution may be varied as desired and the inhibitors may be added to the pickling baths in greater or less proportion than mentioned above. After the pickling operation if the inhibitor oils of the invention are used, the metal treated has a bright surface finish. When using inhibitors formed by treatment of the hereindescribed low boiling fractions, best results are obtained when pickling is carried out at temperatures of about 1GO-165 F., and in the case of inhibitors produced by treatment of high boiling fractions, pickling temperatures may run as high as 19o-195 F. without in any way i'mpairing inhibiting efficiency.

Inhibiting properties of the inhibitors of the invention are demonstrated by the following described tests.

In one series of tests, the pickling baths com- Y prised about 6% H2SO4 solutions containing about 2 pounds of inhibitor per net ton of 66 B. H2504. Temperatures of the pickling solutions were maintained at about 160 F. Low carbon steel strips, from which all scale had been removed, were used. The strips were subjected to half hour pickling, and washed, dried and weighed. Average results of several runs were TABLE 1 Loss in weight, -1/2 hour run Inhibitor A was a water soluble sulfur oil obtained by the herein described sodium dichromate treatment of a water insoluble low boiling fraction (e. g., from receiver 50), and Inhibitor B was a water soluble sulfur oil formed by sodium dichromate treatment of a high boiling fraction (e. g., from receiver 5I). Inhibitor C was the product of Example 3 using nitric acid as the water insoluble sulfur oil treating agent. When no inhibitor was used, the steel strips were pickled under the same conditions except the pickling solutions contained no inhibitor.

The tests o f Table 2 show efficiency of the inhibitors of the invention as compared with a commercially available inhibitor. 'I'he data given were the result of recognized comparative tests which are outlined as follows: Pickling solution contained 8% by weightof 100% HzSO4. Temperatures used were 175 F., 185 F., and 195 F., temperatures which are Just higher than where most inhibitors show a decided break in inhibiting efiiciency. Inhibitor concentrations were .25% and .50% by weight of 100% H2804 in the pickling solution. Metal stri-ps used were low carbon steel cut from the same sheet oi steel. All scale was removed, the strips washed thoroughly. rinsed in water, then in alcohol, dried. and weighed. In each instance the strips were subjected to pickling for one hour. and dried and weighed. Blank uninhibited solutions were returned to their original strength before a second hour of testing. Then all strips were again subjected to pickling for another hour, washed. dried and weighed. To obtain the percentage eiliciency, the grams lost in weight by an uninhibited strip are divided into the grams lost in weight by an. inhibited strip. The result is subtracted from one. and the difference obtained is multiplied by 100, giving a percentage of inhibiting efdciency for that one hour period. Final eiciency rating is the average of two one hour periods of pickling. The factors used in this method of testing are those which follow most closely the generally accepted and used practice found in the production pickling of straight carbon and alloy steels. Experience shows that, as to sulfuric acid inhibiting, under this method an inhibitor must have an average efilciency of or better at .25% concentration at 195 F. to be equal to the accepted good inhibitors on the market. The above test results were:

TABLE 2 Percent Temperature, F.

nc inhibit 115 F. 195F. 195 F.

.25 93.43 93.99 95.91 .25 98.93 81.41 93.34 .5o 91.55 91.99 99.26 rnhibimx .5o 95.54 99.15 91.29

Inhibitor D is the product of Example 1 labove, and Inhibitor X is what is considered, as far as we know, the best commercially available inhibitor used for sulfuric acid pickling.

Water soluble inhibitors of the invention were tested for hydrochloric acid pickling at different temperatures and concentrations to cover various types of muriatic pickling. A solution of 3.75% by weight of HC1 was chosen since the H-ion concentration of such solution generally corresponds with the H-ion concentration of an 8% sulfuric acid solution used in the tests summarized in Table 2. lExcept as to temperatures (shown in Table 3) testing procedure'was the same as that described in the paragraph preceding Table 2. Inhibition emciencies with hydrochloric acid .pickling solutions were TABLE 3 Inhibitor E was a water soluble sulfur oil obtained by the herein described sodium dichromate treatment of a fraction of boiling range of abcit S40-475 F.. e. g., from receiver 5I, except'tne fraction subjected to treatment was obtained by steam distillation at atmospheric pressure of crude initial sulfur oil from tank 26. Inhibitor Y is what is considered, as far as we know, the best commercially available inhibitor for hydrochloric acid pickllng solutions.

The water soluble inhibitors described are suited for use as corrosion inhibitors in arts other than pickling. One phase of the invention involves provision of acid solutions inhibited suiciently to prevent corrosion of metal surfaces which may be contacted by the acid. For example, in the transportation or storage of corrosive mineral acids in metal containers or pipe lines. or in other instances where use of an inhibited acid is desired, a relatively small amount of inhibitor of the invention may be added to the acid to prevent corrosion of metal surfaces. The

, amount of inhibitor used will depend upon the nature and concentration of the acid solution.

We claim:

1. 'I'he process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount or a Water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about '150 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors,-coo1ing the mixture to form a condensate containing water and oil comprising water nsoluble sulfur constituents, treating water insoluble constituents of such oil with an oxidizing agent to convert at least a portion of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

2. The process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dlssociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mix-f ture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with oxidizing agent to convert at least a portion of said sulfur constituents to 'water soluble form, maintaining temperature of the reacting mass during treatment not in excess of about 150 F.,

and recovering water soluble sulfur bearing oil from the reaction mass.

3. The process of pickling metals which cornprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing Water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with oxidizing agent to convert at least a portion of said sulfur constituents to water soluble form, during said treatment maintaining the reaction mass acid and at temperature not in excess of about 150 F., and recovering water soluble sulfur bearing oil from the reaction mass.

4. The process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with oxidizing agent in the presence of mineral acid, to convert at least a portion of said sulfur constituents to water soluble form, the amount of oxidizing agent used being not in excess of about 10% by weight of the reaction mass, and recovering water soluble sulfur bearing oil from the reaction mass.

5. The process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid anda relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble oonstituents of such condensate with hexavalent chromium compound, in the presence of sulfuric acid, to convert at least a portion of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

6. The process of pickling metals which comprises subjecting the metal to theaction of a bath containing mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate comprising water and oil, separating water and oil, dlstilling the oil `to form a condensate comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with hexavalent chromium compound, in the presence of suiicient sulfuric acid to keep chromium in solution, to convert at least a portion-of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

7. The process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate comprising water and oil, separating water and oil, distilling the oil and recovering as condensate a fraction boiling at temperature less than about S40-350 F. and comprising water insoluble sulfur constituents, treating water insoluble constituents of such fraction with hexavalent chromium compound in the presence of suflcient sulfuric acid to keep chromium in solution to convert at least a. portion of said sulfur constituents to ,water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

8. The process of pickling metals which comprises subjecting the metal to the action of a bath containing mineral acid and a relatively small amount of al water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with ald of heat at temperature of not more than about '750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate comprising Water and oil, separating water and oil, distilling the oil and recovering as condensate a fraction boiling at temperature not less than about 340-350 F. and comprising water insoluble sulfur constituents, treating water insoluble constituents of such fraction with hexavalent chromium compound in the presence of sufilcient sulfuric acid to keep chromium in solution to convert at least a portion of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

9. A pickling bath for metals comprising mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about '750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such oil with an oxidizing agent to convert at least a portion of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

10. A pickling bath for metals comprising mineral acid and a relatively small amount of a Water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing Water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with oxidizing agent to convert at least a portion of said sulfur constituents to Water soluble form, during said treatment maintaining the reaction mass acid and at temperature not in excess of about F., and recovering water soluble sulfur bearing oil from the reaction mass.

ll. A pickling bath for metals comprising mineral acid and a relatively small amount of a water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing Water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such condensate with hexavalent chromium compound, in the presence of sulfuric acid, to convert at least a portion of said sulfur constituents to water soluble form, and recovering Water soluble sulfur bearing oil from the resulting reaction mass.

12. A pickling bath for metals comprising mineral acid and a relatively small amount of a Water soluble sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of. hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing water and hydrocarbon oil vapors, cooling the mixture to form a condensate comprising water and oil. separating water and oil, distilling the oil to form a condensate comprising Water insoluble sulfur constituents, treating water insoluble constituents of such condensate with hexavalent chromium compound. in the presence of suicient sulfuric acid to keep chromium in solution, to converT at least a portion of said sulfur constituents tg water soluble fonn, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

13. A pickling bath for metals comprising mineral acid and a relatively small amount of a water soluble `sulfur bearing oil formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes, with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture con-taining water and hydrocarbon oil vapors, cooling the mixture to form a condensate comprising water and oil, separating water and oil, distilllng the oil and recovering as condensate a, fraction boiling at temperature not less than about 340-350 F. and comprising water insoluble sulfur constituents. treating water insoluble constituents of such fraction with hexavalent chromium compound in the presence of suflicient sulfuric acid to keep chromium in solution to convert at least a portion of said sulfur constituents to water soluble form, and recovering water soluble sulfur bearing oil from the resulting reaction mass.

14. A mineral acid solution substantially noncorrosive to metals comprising mineral acid of concentration corrosive to metal and containingel water soluble sulfur bearing oil corrosion inhibitor, said solution being adapted for utilization in operations comprising metal pickling, storage of said solution within confining metal surfaces, and contact of said solution with confining metal surfaces, and said solution containing said oil in quantity to substantially inhibit corrosive action of the acid on metal; said inhibitor being formed by dissociating sludge material, resulting from sulfuric acid treatment of hydrocarbon oil distillate obtained from sulfur containing crudes. with aid of heat at temperature of not more than about 750 F. to break up the sludge under conditions to form a hot gas mixture containing Water and hydrocarbon oil vapors, cooling the mixture to form a condensate containing water and oil comprising water insoluble sulfur constituents, treating water insoluble constituents of such oil with an oxidizing agent to convert at least a portion of said sulfur constituents to water soluble form. and recovering Water soluble 'sulfur bearing oil from the resulting reaction mass.

HENRY F. MERRIAM. GEORGE W. C'U'PIT, JR. 

